• Dielectric and Absorption Filters
  • Standard and customized production in any design
  • Cost effective pricing

Filters are optical elements with specific spectral transmission characteristics. They are used to modify the properties of a light source or to block unwanted wavelengths of light.

There are two different types of filters, depending on the physical principle exploited during the manufacturing process: absorption filters (colour filters) and dielectric filters.

Absorption Filters (Colour Filters)

Absorption filters (colour filters) function on the basis of choosing a glass recipe with chromophoric constituents which absorb a specific range of wavelengths. Typically these are long pass edge filters, but some bandpass types with limited functionality are available. Note that this filter type may fluoresce when used for blocking UV light.


Dielectric Filters

Dielectric filters absorb very little light. The functionality is based on reflection of the unwanted spectral regions based on optical interference within the layer structure of the filter coating. These filters can be manufactured for use in the UV, visible and IR.

In order to reduce the number of coating layers – and thus the cost – a combination may be made by dielectric coating a colour (absorption type) glass substrate. This is common for some bandpass filters.


The following table gives an overview of the main criteria for deciding between these two physical principles of filters.

 

Selection Table Filters:

Physical PrinciplePricePower HandlingAngle ToleranceThicknessDysfunctionsReflectionRoHS-Conform
AbsorptionLowHeating due to absorption: may break at high powerWide angle toleranceLevel of blocking depends on thickness. Typ. 2 – 3mmMay fluorescence when blocking UV lightLowMany types “No” but with “legal” exeption status
DielectricHigh in small volumes. Low to mid in high volumesWithstand high optical power due to low absorptionFunctional spectrum blue shifts with angleMay be very thin eg 0.5mmNoneLow in transmission region. High in blocking regionYes

 

In addition, there are four basic functional types of filters. These are represented below as symbolic transmission curves as a function of wavelength:

 

Functional types:

We offer filters cut to any shape. Black anodized aluminium rings may be provided for ease of mounting.

SpecificationsAbsorption FiltersDielectric Filters
Range of dimensions1mm – 300mm1mm – 300mm
Highest available surface figureλ/4 (DIN: 3/0,5)λ/4 (DIN: 3/0,5)
Highest available surface quality40-20 S/D (DIN: 5/2×0,16)40-20 S/D (DIN: 5/2×0,16)
Highest available tolerance of beam deviation3” (arcsec)3” (arcsec)
BlockingOD3 (standard), OD5 (high blocking)

Dr. Steven Wright

CUSTOMIZED SOLUTIONS

Hannes Heppner

OptiCS

Anja Weets

OPTICS

Rolf Jaspers

Instruments

Hannes Heppner

OptiCS

Dr. Steven Wright

CUSTOMIZED SOLUTIONS